1. Field of the Invention
This invention relates to classifier tanks used for separating particulates, or grit, from a liquid slurry and specifically relates to classifiers constructed to be easily transportable and economically made.
2. Description of Related Art
Grit classifiers are commonly used in a variety of industries, such as mining, municipal wastewater treatment and pulp and paper processing, to process liquid slurries for separation of the solids component from the liquid component of the slurry. More specifically, however, grit classifiers are employed to remove particulate matter or grit from such slurries. xe2x80x9cGritxe2x80x9d typically includes inorganic particulates such as sand, dust or smaller mesh rocks or stones. Grit can also include organic material such as cinders, coffee grounds and other vegetal materials. It is important to the processing of industrial slurries to properly remove the grit from the slurry, and to do so in a manner which will avoid fouling the classifier equipment.
Grit classifiers generally comprise a tank or trough having a screw conveyor or auger positioned therein. The tank or trough is maintained at an angle to the ground. A slurry is introduced into the bottom, or lower, end of the tank, and the screw conveyor is operated to sweep the grit from the reservoir of fluid at the low end of the tank to a solids outlet positioned at the top, or elevated end, of the tank. Many classifier units thus described also act to dewater the grit as the grit is moved by the screw conveyor to the upper portion of the tank. Examples of grit classifiers are disclosed in U.S. Pat. No. 3,865,727 to Broling, et al., U.S. Pat. No. 4,871,449 to Lott and U.S. Pat. No. 5,368,731 to Pesotini.
Conventional grit classifiers are most typically made of a heavy and durable material, such as steel or concrete. They are also conventionally formed of over sixty separate pieces of metal which must then be welded together and secured by fastening means such as screws or bolts. Welding the parts together is very time consuming and, if done incorrectly, can compromise the integrity of the grit classifier. The formation of conventional grit classifiers may typically take about thirty man-hours and may cost several thousand dollars. In addition, the tanks are usually galvanized to increase durability and are then painted with two or more coats of erosion-resistant coatingxe2x80x94all of which adds to the cost of manufacturing the grit classifier and increasing manufacturing time.
Another problem commonly encountered in conventional grit classifiers is that of transportation to a site. That is, grit classifiers are often used in industries where sludge processing systems must be brought to the site, such as in mineral and mining operations, and the transportation of conventional heavy metal or steel classifiers to a site is costly. Heavy lifting equipment (e.g., cranes) and large trucks must be employed to lift, transport and then position conventional grit classifiers at a site. To enable portability of grit classifiers, they have conventionally been manufactured in sections, which provides easier transportation of the parts, but which requires assembly at the site. An example of a grit classifier manufactured in sections is disclosed in U.S. Pat. No. 4,871,449. Assembling the grit classifier on site represents a loss of time and manpower.
Thus, it would be beneficial to the art to provide a grit classifier tank which is configured for simple construction, which is easily transportable to a site, which is resistant to degradation under conventional operating conditions and is economically made and used.
In accordance with the present invention, a grit classifier is unitarily-formed from comparatively lightweight moldable materials which enable the grit classifier to be easily manufactured, easily transported to a site and implemented for use without time-consuming or costly assembly. The construction of the grit classifier of the present invention also renders it durable and corrosion-resistant and also provides beneficial improvements in the grit classifier art by facilitating attachment of a screw conveyor or auger to the grit classifier.
The grit classifier of the present invention comprises a unitarily-formed elongated tank having a bottom and upstanding, continuous wall, a fluid outlet formed at one end of the elongated tank for discharging fluid from the tank and a solids discharge outlet formed at the other end of the tank for discharging grit which has been removed from the fluid component of a slurry. The elongated tank is further structured to support a screw conveyor or auger within the tank for removing the grit or solids component from a slurry introduced into the elongated tank. The tank may be formed with an inlet for introducing a slurry into the tank. The grit classifier may include supports or legs unitarily-formed with the elongated tank, although legs may, alternatively, be added to the tank after formation.
The most beneficial aspect of the present invention is its unitary formation from comparatively lightweight, durable materials which render the grit classifier easily transportable and durable. As used herein, xe2x80x9cunitaryxe2x80x9d or xe2x80x9cunitarily-formedxe2x80x9d means that the tank portion of the grit classifier is formed by means which produce a single component of substantially seamless construction. Depending on the embodiment of the grit classifier of the present invention, the unitarily-formed tank portion may be a single piece or two conjoinable pieces, each of which is unitarily-formed. The present invention thus provides a significant advantage over conventionally-constructed grit classifiers which are constructed of over sixty separate pieces.
The grit classifier of the present invention may be made by any suitable technique which produces a unitarily-formed structure as described herein. A particularly suitable example of such manufacturing means is a rotational molding process using high molecular weight plastics, such as polyethylene, or resinous materials. Rotational molding is a known process which involves introducing flowable plastic or plastic-like materials into a clamshell mold formed to the desired three-dimensional product design and continuously rotating the mold to assure the complete filling of the mold. The clamshell mold is then removed once the plastic has cured and hardened. Other suitable methods may be employed, however. By forming the grit classifier of the present invention in a unitarily-formed construction, there is a significant decrease in cost of manufacture, a significant decrease in manufacturing time (from weeks to days), an elimination of the need for coating the grit classifier because of the durability of the plastic material and a significant decrease in transportation costs and setup time at a given site.
One embodiment of the present invention comprises a single-walled tank of unitary formation which may have support legs additionally molded therewith or, in the alternative, secured to the bottom of the tank thereafter. In a second embodiment of the invention, the tank body is constructed with a double wall having a space therebetween which may be filled at the site with a weighted material, such as heavy-weight foam or cementitious material, to provide added stability to the grit classifier. The tank body may also be formed in two separate sections, generally comprising a pool section and grit discharge section with extension, which allows the discharge section of the grit classifier to be selectively sized for a particular application.
These and other advantages of the present invention will be better understood with reference to the detailed description of the illustrated embodiments disclosed hereafter.